It is oftentimes desirable, and sometimes necessary, that certain indications be made in a form other than in a conventional display that requires use of sight. In the conventional hand-held electronic calculator, for example, it is common to display the calculator result on a visual display, normally light-emitting diodes.
While visual readouts may be satisfactory where the user has either the faculty of sight or has few visual diversions (which might not be true, for example, when visual observations must be made of other equipment or factors), equipment usefulness could be enhanced if a non-visual indication could be provided. A non-visual, or sightless, indicating system is particularly useful, of course, in that it enables a blind person to use such equipment.
It has heretofore been suggested that voice indications could be provided for apparatus such as a digital voltmeter or a drum-type counter indicator (see, for example, U.S. Pat. Nos. 3,081,431 and 3,163,819). It has also been suggested that an indicator can be provided to produce a limited number of tones of different frequency to establish value ranges or conditions (see, for example, U.S. Pat. Nos. 3,355,706, 3,089,119 and 3,346,857). In addition, it has heretofore been suggested that an audio output could be provided having a frequency that varies with measured resistance for uses such as testing equipment and frequency generator circuitry (see, for example, U.S. Pat. Nos. 3,689,832 and 3,758,855).
Such devices have not, however, proved to be completely successful in providing audible indications for at least some equipment, including electronic calculators. In addition, no known apparatus proved to be completely suitable for providing audible output signals in equipment usable by blind persons, and no known apparatus has been completely successful in indicating digital information in audible form that includes a plurality of audible output signals at the same frequency.